Bipolar transistor integrated with metal gate cmos devices

ABSTRACT

A high-k gate dielectric layer and a metal gate layer are formed and patterned to expose semiconductor surfaces in a bipolar junction transistor region, while covering a CMOS region. A disposable material portion is formed on a portion of the exposed semiconductor surfaces in the bipolar junction transistor area. A semiconductor layer and a dielectric layer are deposited and patterned to form gate stacks including a semiconductor portion and a dielectric gate cap in the CMOS region and a cavity containing mesa over the disposable material portion in the bipolar junction transistor region. The disposable material portion is selectively removed and a base layer including an epitaxial portion and a polycrystalline portion fills the cavity formed by removal of the disposable material portion. The emitter formed by selective epitaxy fills the cavity in the mesa.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.12/556,205, filed Sep. 9, 2009 the entire content and disclosure ofwhich is incorporated herein by reference.

BACKGROUND

The present invention relates to semiconductor devices, and particularlyto bipolar complementary metal-oxide-semiconductor (BiCMOS) integratedstructures including a bipolar transistor having a self-aligned baseformed by selective epitaxy and complementary metal-oxide-semiconductor(CMOS) devices having a metal gate and a high-k gate dielectric andmethods of manufacturing the same.

One of the key technological innovations for improving performance ofCMOS devices has been the introduction of high dielectric constant(high-k) dielectric materials for the gate dielectric of field effecttransistors. The high-k dielectric materials include dielectric metaloxides that have a dielectric constant greater than 3.9, which is thedielectric constant of silicon oxide. Typically, such high-k dielectricmaterials have a dielectric constant greater than 7.5.

Performance of advanced CMOS transistors is further enhanced byemploying a metal gate, which refers to a gate electrode including ametal layer, i.e., a layer of an elemental metal or an intermetalliccompound that is not an alloy of silicon. The metal gate increases theconductive of the gate electrode of a transistor so that the RC delay ofthe gate electrode is reduced compared with a gate electrode employing adoped semiconductor material and/or a metal-semiconductor alloy such asa silicide.

Use of a high-k gate dielectric and/or a metal gate introducestremendous difficulties in integration with bipolar devices because thepatterning of the high-k dielectric material requires dedicatedpatterning processes that are not compatible with existing processes formanufacturing a bipolar junction transistor. Additional processing stepsintroduced to enable integration of bipolar junction transistors withCMOS devices employing a high-k gate dielectric and/or a metal gate tendto drive up the complexity of the overall processing sequence and thecost of manufacturing BiCMOS devices. Manufacturable integration schemesfor BiCMOS devices including a high-k gate dielectric and/or a metalgate require a minimal number of additional processing steps.

BRIEF SUMMARY

In an embodiment of the present invention, a high-k gate dielectriclayer and a metal gate layer are formed and patterned to exposesemiconductor surfaces in a bipolar junction transistor region, whilecovering a CMOS region. A disposable material portion is formed on oneof the exposed semiconductor surfaces, which is a surface of asemiconductor region that is surrounded by a shallow trench isolationstructure in the bipolar junction transistor area. A semiconductor layerand a dielectric layer are deposited and patterned to form gate stacksincluding a semiconductor portion and a dielectric gate cap in the CMOSregion and a cavity containing mesa over the disposable material portionin the bipolar junction transistor region. The disposable materialportion is selectively removed and a base layer including an epitaxialportion and a polycrystalline portion fills the cavity formed by removalof the disposable material portion. The emitter formed by selectiveepitaxy fills the cavity in the mesa. The feedthrough to a subcollectorlayer may be provided by the same ion implantation as the source/drainion implantation.

According to an aspect of the present invention, a method of forming asemiconductor structure is provided, which comprises:

forming a high dielectric constant (high-k) dielectric material layerhaving a dielectric constant greater than 3.9 on a surface of asemiconductor layer;

removing the high-k dielectric layer from a portion of the surface ofthe semiconductor layer and forming a disposable material portion on theportion of the surface of the semiconductor layer;

forming a semiconductor material layer and a dielectric cap materiallayer over the high-k dielectric material layer and the disposablematerial layer;

patterning the dielectric cap material layer and the semiconductormaterial layer to form at least one gate stack and a mesa structure thatlaterally surrounds a cavity, wherein the at least one gate stackincludes a portion of the high-k dielectric layer and the mesa structurecomprises a remaining portion of the dielectric cap material layer and aremaining portion of the semiconductor material layer, and a top surfaceof the disposable material portion is exposed within the cavity;

expanding the cavity by removing the disposable material portionunderneath the mesa structure to expose the top surface of thesemiconductor layer; and

growing an epitaxial base in a portion of the cavity by selectiveepitaxy.

According to another aspect of the present invention, a semiconductorstructure is provided, which comprises:

at least one metal-oxide-semiconductor (MOS) transistor located on afirst portion of a semiconductor substrate, the at least one MOStransistor including a high dielectric constant (high-k) gate dielectrichaving a dielectric constant greater than 3.9; and

a bipolar junction transistor (BJT) located on a second portion of thesemiconductor substrate, the BJT including a collector located in thesemiconductor substrate and laterally surrounded by at least one shallowtrench isolation structure, an epitaxial base located on the collector,a first polycrystalline extrinsic base portion contacting an entirety ofsidewalls of the epitaxial base, a second polycrystalline extrinsic baseportion contacting an entirety of outer sidewalls of the firstpolycrystalline extrinsic base portion, and an emitter contacting theepitaxial base and the first polycrystalline extrinsic base portion butnot contacting the second polycrystalline extrinsic base portion.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view of an exemplary structureaccording to an embodiment of the present invention after formation of ahigh dielectric constant (high-k) dielectric material layer, a metallayer, and a first semiconductor material layer.

FIG. 2 is a vertical cross-sectional view of the exemplary structureafter deposition of a disposable material layer.

FIG. 3 is a vertical cross-sectional view of the exemplary structureafter patterning of the disposable material layer to form a disposablematerial portion.

FIG. 4 is a vertical cross-sectional view of the exemplary structureafter deposition of a second semiconductor material layer and adielectric cap material layer.

FIG. 5 is a vertical cross-sectional view of the exemplary structureafter patterning of gate stacks and a mesa structure and formation offirst gate spacers, a first inner spacer, and a first outer spacer.

FIG. 6 is a vertical cross-sectional view of the exemplary structureduring ion implantation of ions through the mesa structure or the cavityin the mesa structure to form a collector.

FIG. 7 is a vertical cross-sectional view of the exemplary structureafter formation of second gate spacers, a second inner spacer, and asecond outer spacer.

FIG. 8 is a vertical cross-sectional view of the exemplary structureafter formation of source and drain regions of a first conductivity typeand a subcollector feedthrough.

FIG. 9 is a vertical cross-sectional view of the exemplary structureafter formation of source and drain regions of a second conductivitytype.

FIG. 10 is a vertical cross-sectional view of the exemplary structureafter formation of a buffer dielectric layer and a stress-generatinglayer.

FIG. 11 is a vertical cross-sectional view of the exemplary structureafter a first patterning of the buffer dielectric layer and thestress-generating layer.

FIG. 12 is a vertical cross-sectional view of the exemplary structureafter expanding the cavity in the mesa structure by removing thedisposable material portion.

FIG. 13 is a vertical cross-sectional view of the exemplary structureafter a selective epitaxy that forms an epitaxial base and a firstpolycrystalline extrinsic base portion.

FIG. 14 is a vertical cross-sectional view of the exemplary structureafter a selective epitaxy that forms an emitter.

FIG. 15 is a vertical cross-sectional view of the exemplary structureafter a second patterning of the buffer dielectric layer and thestress-generating layer.

FIG. 16 is a vertical cross-sectional view of the exemplary structureafter an activation anneal and the removal of the buffer dielectriclayer and the stress-generating layer.

FIG. 17 is a vertical cross-sectional view of the exemplary structureafter removal of gate dielectric caps and a dielectric cap material mesaportion.

FIG. 18 is a vertical cross-sectional view of the exemplary structureafter formation of an upper spacer, a lower spacer, and an outer gatespacer.

FIG. 19 is a vertical cross-sectional view of the exemplary structureafter formation of a middle-of-line (MOL) dielectric layer and contactvias.

DETAILED DESCRIPTION

The present invention, which provides BiCMOS integrated structuresincluding a bipolar transistor including a self-aligned base formed byselective epitaxy and CMOS devices having a metal gate and a high-k gatedielectric and methods of manufacturing the same, will now be describedin more detail by referring to the accompanying drawings. Like andcorresponding elements are referred to by like reference numerals in thedrawings.

Referring to the vertical cross-sectional view of FIG. 1, an exemplarysemiconductor structure according to an embodiment of the presentinvention includes a semiconductor substrate 8, a high dielectricconstant (high-k) dielectric material layer 40L, a metal layer 42L, andan optional first semiconductor material layer 44L. The exemplarysemiconductor structure may be formed by providing a semiconductorsubstrate including a single crystalline semiconductor layer 10. Atleast one shallow trench isolation structure 20 and a subcollectorregion 32 are formed in the semiconductor substrate 8.

The single crystalline semiconductor layer 10 includes a singlecrystalline, i.e., epitaxial, semiconductor material, which may beselected from, but is not limited to, silicon, germanium,silicon-germanium alloy, silicon carbon alloy, silicon-germanium-carbonalloy, gallium arsenide, indium arsenide, indium phosphide, III-Vcompound semiconductor materials, II-VI compound semiconductormaterials, organic semiconductor materials, and other compoundsemiconductor materials. Typically, the single crystalline semiconductorlayer 10 is a single crystalline silicon material. The doping of thesingle crystalline semiconductor layer 10 as provided in thesemiconductor substrate 8 may be optimized for device performance.

The subcollector region 32 is formed by implanting dopant of a firstconductivity type into the single crystalline semiconductor layer 10 byion implantation employing an implantation mask. The first conductivitytype may be p-type of n-type. While the present invention is describedfor the case in which the first conductivity type is n-type, embodimentsin which the first conductivity type is p-type may also be employed. Thedepth of the upper surface 32U of the subcollector region 32 may be from100 nm to 500 nm, and preferably from 150 nm to 400 nm. The uppersurface 32U of the subcollector region 32 is the interface between thesubcollector region 32 and portions of the single crystallinesemiconductor layer 10 located above the single crystallinesemiconductor layer 10. The thickness of the subcollector region may befrom 100 nm to 600 nm, although lesser and greater thicknesses may alsobe employed.

The single crystalline semiconductor layer 10 may be doped with dopantsof a second conductivity type, which is the opposite of the firstconductivity type. For example, the second conductivity type is a p-typeif the first conductivity type is n-type, and vice versa. A firstconductivity type doped well 12 may be formed by converting a portion ofthe single crystalline semiconductor layer 10 into a region having adoping of the first conductivity type by ion implantation.

For the purposes of description of the present invention, the regions ofthe exemplary semiconductor structure are divided into an emitter-baseregion EBR, a collector feedthrough region CFTR, an n-type field effecttransistor (NFET) region NFETR, and a p-type field effect transistor(PFET) region. The exemplary semiconductor structure may include aplurality of any of emitter-base regions, collector feedthrough regions,n-type field effect transistor regions, and p-type field effecttransistor regions, and may also include regions for any other type ofsemiconductor devices. The emitter-base region EBR and the collectorfeedthrough region CFTR are collectively referred to as a bipolarjunction transistor (BJT) region BJTR, and the NFET region NFETR and thePFET region PFETR are collectively referred to as a complementarymetal-oxide-semiconductor (CMOS) region CMOSR.

The at least one shallow trench isolation structure 20 is formed by anetch that forms trenches in the single crystalline semiconductor layer10. The trenches extend from the top surface of the single crystallinesemiconductor layer 10 to a depth, which is preferably greater than thedepth of the upper surface 32U of the subcollector region 32. The depthof the trenches may be from 150 nm to 700 nm, and preferably from 200 nmto 600 nm, although lesser and greater depths may also be employed. Thetrenches are filled with a dielectric material such as silicon oxide,silicon nitride, silicon oxynitride, or a combination thereof, which issubsequently planarized to form the at least one shallow trenchisolation structure 20.

Various semiconductor regions laterally surrounded by the at least oneshallow trench isolation structure are provided in the exemplarysemiconductor structure. For example, a first semiconductor regioncomprising the single crystalline semiconductor material and laterallysurrounded by the at least one shallow trench isolation region 20 andlocated above the subcollector region 20 is provided in the emitter-baseregion EBR. A second semiconductor region comprising the singlecrystalline semiconductor material and laterally surrounded by the atleast one shallow trench isolation region 20 and located above thesubcollector region 20 is provided in the collector feedthrough regionCFTR. The first semiconductor region and the second semiconductor regionare portions of the single crystalline semiconductor layer 10. A thirdsemiconductor region having a doping of the second conductivity type,laterally surrounded by the at least one shallow trench isolationstructure 20, and constituting a portion of the single crystallinesemiconductor layer 10 is provided in the NFET region NFETR. A fourthsemiconductor region having a doping of the first conductivity type,laterally surrounded by the at least one shallow trench isolationstructure 20, and constituting a portion of the first conductivity typedoped well 12 is provided in the PFET region PFETR.

A high dielectric constant (high-k) dielectric material layer 40L isformed on a top surface of the semiconductor substrate 8. The high-kdielectric material layer 40L comprises a high dielectric constant(high-k) material comprising a dielectric metal oxide and having adielectric constant that is greater than the dielectric constant ofsilicon oxide of 3.9. Preferably, the dielectric metal oxide has adielectric constant that is greater than the dielectric constant ofsilicon nitride of 7.5. The high-k dielectric material layer 40L may beformed by methods well known in the art including, for example, chemicalvapor deposition (CVD), atomic layer deposition (ALD), molecular beamdeposition (MBD), pulsed laser deposition (PLD), liquid source mistedchemical deposition (LSMCD), etc.

The dielectric metal oxide comprises a metal and oxygen, and optionallynitrogen and/or silicon. Exemplary high-k dielectric materials includeHfO₂, ZrO₂, La₂O₃, Al₂O₃, TiO₂, SrTiO₃, LaAlO₃, Y₂O₃, HfO_(x)N_(y),ZrO_(x)N_(y), La₂O_(x)N_(y), Al₂O_(x)N_(y), TiO_(x)N_(y),SrTiO_(x)N_(y), LaAlO_(x)N_(y), Y₂O_(x)N_(y), a silicate thereof, and analloy thereof. Each value of x is independently from 0.5 to 3 and eachvalue of y is independently from 0 to 2. The thickness of the high-kdielectric material layer 40L may be from 1 nm to 10 nm, and preferablyfrom 1.5 nm to 3 nm. The high-k dielectric material layer 40L may havean effective oxide thickness (EOT) on the order of, or less than, 1 nm.

A metal layer 42L is deposited directly on the top surface of the high-kdielectric material layer 40L. The metal layer 42L may be formed, forexample, by chemical vapor deposition (CVD), physical vapor deposition(PVD), or atomic layer deposition (ALD). The metal layer 42L has amaterial that is an elemental metal, a metallic alloy, a conductivemetallic nitride, or a conductive metallic carbide.

In one embodiment, the material of the metal layer 42L may be aconductive transition metal nitride or a conductive transition metalcarbide. The first metallic compound is a compound of a first metallicelement selected from transition metals and a non-metallic element. Ifthe non-metallic element is nitrogen, the first metallic compound is atransition metal nitride. If the non-metallic element is carbon, thefirst metallic compound is a transition metal carbide. For example, thefirst metallic compound may be selected from TiN, TiC, TaN, TaC, and acombination thereof. As used herein, transition metals include elementsfrom Group 3B, 4B, 5B, 6B, 7B, 8B, 1B, and 2B and Lanthanides andActinides in the Periodic Table of the Elements. The thickness of themetal layer 42L may be from 1 nm to 10 nm, and preferably from 3 nm to10 nm, although lesser and greater thicknesses are also contemplatedherein.

In another embodiment, the material of the metal layer 42L may include ametal in elemental form. Typical elemental metals that may be selectedfor the metal layer 42L include, but are not limited to, Al, Be, Mg, Ca,Sr, Ba, Sc, Y, La, Ti, Zr, Hf, Dy, Lu, Er, Pr, and Ce. The elementalmetal may consist of at least one alkaline earth metal. Alternately, themetal layer 42L consists of at least one transition metal. Yetalternately, the metal layer 42L may consist of a mixture of at leastone alkaline earth metal and at least one transition metal. Preferably,the thickness of the metal layer 42L is from 0.1 nm to 3.0 nm, althoughlesser and greater thicknesses are also contemplated herein.

An optional first semiconductor material layer 44L is deposited directlyon the top surface of the metal layer 42L, for example, by low pressurechemical vapor deposition (LPCVD), rapid thermal chemical vapordeposition (RTCVD), or plasma enhanced chemical vapor deposition(PECVD). The formation of the optional first semiconductor materiallayer 44L is may, or may not, be present in the exemplary semiconductorstructure of the present invention. The optional first semiconductormaterial layer 44L comprises a polycrystalline or amorphoussemiconductor material. For example, the optional first semiconductormaterial layer 44L may comprise polysilicon, a polycrystalline silicongermanium alloy, a polycrystalline silicon carbon alloy, or apolycrystalline silicon germanium carbon alloy.

In one embodiment, the optional first semiconductor material layer 44Lmay be formed as a doped polycrystalline semiconductor layer throughin-situ doping. Alternately, the optional first semiconductor materiallayer 44L may be deposited as an intrinsic semiconductor material, andis subsequently doped by ion implantation of dopant atoms prior topatterning of gate electrodes. The thickness of the optional firstsemiconductor material layer 44L may be from 5 nm to 200 nm, andtypically from 20 nm to 50 nm, although lesser and greater thicknessesmay also be employed.

Referring to FIG. 2, the vertical stack of the optional firstsemiconductor material layer 44L, the metal layer 42, and the high-kdielectric material layer 40L is lithographically patterned to exposethe top surfaces of the single crystalline semiconductor layer 10 in theBJT region BJTR. However, the vertical stack of the optional firstsemiconductor material layer 44L, the metal layer 42, and the high-kdielectric material layer 40L covers the top surfaces of the singlecrystalline semiconductor layer 10 in the CMOS region CMOSR.

A disposable material layer 43L is deposited directly on the topsurfaces of the first semiconductor region and the second semiconductorregion within the BJT region BJTR. The disposable material layer 43Lcomprises a disposable material that may be removed selective to thesemiconductor material of the first semiconductor region, which is thematerial of the single crystalline semiconductor layer 10. Preferably,the disposable material layer 43L comprises a disposable material thatmay be removed selective to the dielectric material of the at least oneshallow trench isolation structure 20 and the dielectric material of adielectric cap material layer and the dielectric material of astress-generating dielectric material layer that are subsequentlyformed. Typically, the dielectric cap material layer and thestress-generating dielectric material layer comprise silicon nitride.

In one embodiment, the disposable material layer 43L is a doped silicateglass such as borosilicate glass, which has a higher etch rate that theetch rate of undoped silicate glass that is typically employed for theat least one shallow trench isolation structure 20. Depending on thedoping of the doped silicate glass, the doped silicate glass may have anetch rate that is 3-10 times the etch rate of an undoped silicate glassemployed in the at least one shallow trench isolation structure 20. Anexemplary etch chemistry for etching the doped silicate glass is ahydrofluoric-acid-based etch chemistry.

In another embodiment, the disposable material layer 43L is germanium ora silicon-germanium alloy having a germanium concentration greater than25%, and preferably greater than 70%. In this case, the semiconductormaterial of the first semiconductor region is typically a singlecrystalline silicon. Germanium or a silicon-germanium alloy may beremoved selective to silicon. Typically, the etch selectivity of asilicon-germanium alloy relative to silicon increases with theconcentration of germanium in the silicon-germanium alloy.

Referring to FIG. 3, the disposable material layer 43L islithographically patterned by employing a first photoresist 41 and anetch to form a disposable material portion 43 directly on the topsurface of the first semiconductor region in the emitter-base regionEBR. The disposable material layer 43L is removed in the collectorfeedthrough region CFTR and the CMOS region CMOSR. The entirety of theperiphery of the disposable material portion 43 overlies at least oneshallow trench isolation structure 20 that laterally surrounds the firstsemiconductor region, i.e., the portion of the single crystallinesemiconductor layer 10 located above the subcollector region 32 and inthe emitter-base region EBR. The thickness of the disposable materiallayer 43L may be from 5 nm to 200 nm, and preferably from 20 nm to 50nm, although lesser and greater thicknesses may also be employed. Thefirst photoresist 41 is subsequently removed, for example, by ashing.

Referring to FIG. 4, a second semiconductor material layer 46L and adielectric cap material layer 49L are deposited directly on thedisposable material portion 43 and the exposed surfaces of the optionalfirst semiconductor material layer 44L and/or the metal layer 42L. Thesecond semiconductor material layer 46L may comprise any semiconductormaterial provided that the material of the disposable material portion43 may be removed selective to the material of the second semiconductormaterial layer 46L. For example, the second semiconductor material layer46L may comprise polysilicon, a polycrystalline silicon germanium alloy,a polycrystalline silicon carbon alloy, or a polycrystalline silicongermanium carbon alloy. If the disposable material portion 43 comprisesgermanium, the second semiconductor material layer 46L preferablycomprises polysilicon.

The second semiconductor material layer 46L has a doping of the firstconductivity type, i.e., the conductivity type that is the opposite ofthe conductivity type of the subcollector region 32. The secondsemiconductor material layer 46L may be formed, for example, by lowpressure chemical vapor deposition (LPCVD), rapid thermal chemical vapordeposition (RTCVD), or plasma enhanced chemical vapor deposition(PECVD). The thickness of the second semiconductor material layer 46Lmay be from 20 nm to 200 nm, and preferably from 40 nm to 100 nm,although lesser and greater thicknesses may also be employed.

The dielectric cap material layer 49L comprises a dielectric material.Preferably, the dielectric cap material layer 49L comprises siliconnitride. The dielectric cap material layer may be formed, for example,by low pressure chemical vapor deposition (LPCVD), rapid thermalchemical vapor deposition (RTCVD), or plasma enhanced chemical vapordeposition (PECVD). The thickness of the dielectric cap layer 49L may befrom 10 nm to 150 nm, and preferably from 20 nm to 100 nm, althoughlesser and greater thicknesses may also be employed.

Referring to FIG. 5, the vertical stack of the dielectric cap materiallayer 49L, the second semiconductor material layer 46L, the optionalfirst semiconductor material layer 44L, the metal layer 42L, and thehigh-k dielectric material layer 40L is lithographically patterned toform a mesa structure in the emitter-base region EBR and gate stacks 50in the NFET region NFETR and in the PFET region PFETR. Preferably, theetch process employed to pattern the high-k dielectric material layer40L is selective to the semiconductor material of the single crystallinesemiconductor layer 10. Preferably, the etch processes employed topattern the optional first semiconductor material layer 44L, the metallayer 42L, and the high-k dielectric material layer 40L are selective tothe material of the disposable material portion 43.

Each gate stack 50 includes a dielectric gate cap 49, a secondsemiconductor material portion 46, an optional first semiconductormaterial portion 44, a metal portion 42, and a high dielectric constant(high-k) gate dielectric 40. The sidewalls of the various materialportions (49, 46, 44, 42, 40) in each gate stack 50 are verticallycoincident, i.e., located in a same vertical plane.

The mesa structure includes a vertical stack of a remaining portion ofthe second semiconductor material layer 46L in the emitter-base regionEBR, which is herein referred to as a second polycrystalline extrinsicbase portion 48, and a remaining portion of the dielectric cap materiallayer 49L in the emitter-base region EBR, which is herein referred to asa dielectric cap material mesa portion 51. The mesa structure (48, 51)is ring-shaped and laterally surrounds a cavity 69, which is locatedabove a center portion of the disposable material portion 43. The cavityoverlies a center portion of the first semiconductor region. The topsurface of the disposable material portion 43 is exposed within thecavity 69.

The second semiconductor material portions 46 have the same thicknessand the same composition as the second polycrystalline extrinsic baseportion 48. The dielectric gate caps 49 have the same thickness and thesame composition as the dielectric cap material mesa portion 51. Theentirety of the outer periphery of the mesa structure (48, 51) overliesthe at least one shallow trench isolation structure 20. The entirety ofthe inner periphery of the mesa structure (48, 51) overlies the firstsemiconductor region, which is the portion of the single crystallinesemiconductor layer 10 that is located above the subcollector region 32and in the emitter-base region EBR.

Various source and drain extension regions (not shown) may be formed byemploying at least one masked ion implantation. Various haloimplantations may be performed as needed employing at least anothermasked ion implantation.

A dielectric material layer is deposited and anisotropically etched toform first gate spacers 54, a first inner spacer 52, and a first outerspacer 53. Each of the first gate spacers 54 contacts and laterallysurrounds a gate stack (40, 43, 44, 46, 49). The first inner spacer 52is a first inner mesa spacer formed directly on the inner sidewalls ofthe mesa structure (48, 51). The first outer spacer 53 is a first outermesa spacer formed directly on the outer sidewalls of the mesa structure(48, 51), and laterally abuts and surrounds the mesa structure (48, 51).The first gate spacers 54, the first inner spacer 52, and the firstouter spacer 53 comprise a first dielectric material and have a firstlateral width. In other words, the first gate spacers 54, the firstinner spacer 52, and the first outer spacer 53 have a same compositionand a same lateral thickness as measured at the bottom of each spacer.The first dielectric material may be silicon oxide, and the firstlateral width may be from 10 nm to 100 nm, although lesser and greaterlateral widths may also be employed.

Referring to FIG. 6, a second photoresist 35 is applied to the topsurfaces of the exemplary semiconductor structure and lithographicallypatterned to form an opening over the disposable material portion 43 inthe emitter-base region EBR. First ions of the first conductivity type,which is the conductivity of the dopants of the subcollector region 32,may be implanted through the cavity in the mesa structure (48, 51) intoa center portion of the first semiconductor region in the emitter-baseregion EBR. In this case, the mesa structure (48, 51) including thecavity 69 is employed as a self-aligning mask for the first ions. Inother words, the mesa structure (48, 51) self-aligns the first ions byletting only the first ions that pass through the cavity 69. The path ofthe first ions is schematically shown as I/I_1. In addition, second ionsof the first conductivity type may be implanted through the opening inthe second photoresist 35 into the first semiconductor region in theemitter-base region EBR. In this case, the second photoresist 35 isemployed as the masking layer for the second ions. The path of thesecond ions is schematically shown as I/I_2. In case the firstconductivity type is n-type, first and second ions may be selected fromions of P, As, and Sb. In case the second conductivity type is p-type,first and second ions may be selected from B, Ga, and In.

The first semiconductor region after the implantation of the firstand/or second ions is doped with dopants of the first conductivity type,and constitutes a collector 30 of a bipolar junction transistor. Thecollector 30 vertically abuts the subcollector region 32. are implantedinto ion implantation of ions through the mesa structure or the cavityin the mesa structure to form a collector.

The doping concentration of the collector 30 is in the range from1.0×10¹⁸/cm³ to 1.0×10²¹/cm³, and preferably from 1.0×10¹⁹/cm³ to1.0×10²⁰/cm³. The doping profile and the thickness of the collector 30are optimized for transistor performance. The subcollector region 32 isheavily doped with the same type dopants as the collector 30, typicallyat a concentration on the order of 1.0×10²¹/cm³. The second photoresist35 is subsequently removed.

Referring to FIG. 7, another dielectric material layer is deposited andanisotropically etched to form second gate spacers 58, a second innerspacer 56, and a second outer spacer 57. Each of the second gate spacers58 contacts and laterally surrounds a first gate spacer 54. The secondinner spacer 56 is a second inner mesa spacer formed directly onsidewalls of the first inner spacer 52 within the cavity 69. The secondouter spacer 57 is a second outer mesa spacer formed directly on theouter sidewalls of the first outer spacer 53, and laterally abuts andsurrounds the first outer spacer 53. The second gate spacers 58, thesecond inner spacer 56, and the second outer spacer 57 have a samecomposition and a same lateral thickness as measured at the bottom ofeach spacer. For example, the second gate spacers 58, the second innerspacer 52, and the second outer spacer 57 may comprise silicon nitride.

Referring to FIG. 8, a third photoresist 37 is applied to the topsurfaces of the exemplary semiconductor structure and lithographicallypatterned to cover the emitter-base region EBR and the PFET regionPFETR. The third photoresist 37 is removed in the collector feedthroughregion CFTR and in the NFET region NFETR by lithographic patterning.

Ions of the first conductivity type are implanted into the semiconductorsubstrate 8 employing the third photoresist 37 as an implantation masklayer. A subcollector feedthrough 31 is formed in the implanted portionof the single crystalline semiconductor layer 10 in the collectorfeedthrough region CFTR, and source and drain regions 22 of the firstconductivity type are formed in the NFET region NFETR. The subcollectorfeedthrough 31 contacts the subcollector region 32, and extends from thesubcollector region 32 to the top surface of the single crystallinesemiconductor layer 10, which is the top surface of the substrate 8.

The bottom portions of the source and drain regions 22 in the NFETregion NFETR have a same doping as the subcollector feedthrough 31. Anydifference in doping concentration between the subcollector feedthrough31 and the source and drain regions 22 in the NFET region NFETR is dueto the additional dopants previously introduced into the singlecrystalline semiconductor layer 10 in the NFET region during formationof source and drain extension regions, which are limited in extent tothe upper portion of the source and drain regions 22 in the NFET regionNFETR. The third photoresist 37 is subsequently removed, for example, byashing. Embodiments in which the subcollector feedthrough 31 and thesource and drain regions 22 of the first conductivity type are formed inseparate steps employing two separate photoresists may also be employed.

Referring to FIG. 9, a fourth photoresist 39 is applied to the topsurfaces of the exemplary semiconductor structure and lithographicallypatterned to cover the emitter-base region EBR, the collectorfeedthrough region CFTR, and the NFET region NFETR. The fourthphotoresist 39 is removed in the PFET region PFETR by lithographicpatterning.

Ions of the second conductivity type are implanted into the firstconductivity type doped well 12 employing the fourth photoresist 39 asan implantation mask layer. Source and drain regions 24 of the secondconductivity type are formed in the PFET region PFETR. The fourthphotoresist 39 is subsequently removed, for example, by ashing.

Referring to FIG. 10, a buffer dielectric layer 62 and astress-generating layer 64 are deposited on the exposed surfaces of theexemplary semiconductor structure. The buffer dielectric layer 62 isformed directly on the top surfaces of the semiconductor substrate 8,and comprises a material that promotes adhesion of the stress-generatinglayer 64. For example, the buffer dielectric layer 62 may be a siliconoxide layer. The thickness of the buffer dielectric layer 62 may be from1 nm to 30 nm, although lesser and greater thicknesses may also beemployed.

The stress-generating layer 64 comprises a stress-generating material,which may be a tensile-stress-generating dielectric material or acompressive-stress-generating dielectric material. For example, thestress-generating layer 64 may be a tensile-stress-generating nitridelayer or a compressive-stress-generating nitride layer. While thisembodiment of the present invention is described for a case in which thestress-generating layer 64 is a tensile-stress-generating dielectricmaterial, which generates a tensile stress in the portion of the singlecrystalline semiconductor layer 10 located directly underneath,embodiments in which the stress-generating layer 64 is acompressive-stress-generating dielectric material may also be employed.The stress-generating layer 64 may generate a stress on the order of 0.5GPa to 5.0 GPa in the portions of the single crystalline semiconductorlayer 10 located directly underneath depending on the geometry of thegate stacks 50. The thickness of the stress-generating layer 64 may befrom 10 nm to 100 nm, although lesser and greater thicknesses may beemployed.

Referring to FIG. 11, a fifth photoresist 65 is applied to the topsurfaces of the exemplary semiconductor structure, and islithographically patterned to cover the collector feedthrough regionCFTR, the NFET region NFETR, and the PFET region PFETR. The fifthphotoresist 65 is removed from the emitter-base region EBR. Thestress-generating layer 64 and the buffer dielectric layer 62 areremoved from the emitter-base region EBR by at least one etch whileemploying the fifth photoresist 65 as an etch mask.

Referring to FIG. 12, the cavity 69 located in, and surrounded by, themesa structure (48, 51) is expanded by removing the disposable materialportion 43 from underneath. Because the mesa structure (48, 51) coversperipheral portions of the disposable material portion 43, thedisposable material portion 43 is removed from underneath the mesastructure (48, 51). The top surface of the collector 30, which comprisesa single crystalline semiconductor material having a doping of the firstconductivity type, is exposed at the bottom of the cavity 69 asexpanded. Sidewall surfaces and a bottom surface 69X the secondpolycrystalline extrinsic base portion 48 are exposed in the expandedcavity 69. The exposed bottom surface 69X of the second polycrystallineextrinsic base portion 48 is a horizontal surface of the secondpolycrystalline extrinsic base portion 48 that is located above the topsurface of the semiconductor substrate 8. The second inner spacer 56and/or the first inner spacer 52 are undercut with the expansion of thecavity 69. The removal of the disposable material portion 43 may beeffected by an etch that is selective to the material of the collector30 and the materials of the dielectric cap material mesa portion 51 andthe stress-generating layer 64.

Referring to FIG. 13, a selective epitaxy is performed to simultaneouslygrow an epitaxial base 60A and a first polycrystalline extrinsic baseportion 60B in a portion of the cavity 69. The growth of the epitaxialbase 60A and the first polycrystalline extrinsic base portion 60B is aselective epitaxy process in which a reactant and an etchant are flowedinto a processing chamber concurrently or alternately. The parameters ofthe selective epitaxy are selected so that no semiconductor material isdeposited on dielectric surfaces such as the surfaces of thestress-generating layer 64, the dielectric cap material mesa portion 51,the buffer dielectric layer 62, the at least one shallow trenchisolation structure 20, the first inner spacer 52, the second innerspacer 56, the first outer spacer 53, and the second outer spacer 57.Deposition of a semiconductor material on semiconductor surfaces isenabled because nucleation and deposition of the semiconductor materialoccurs at a greater rate on the semiconductor surfaces such as theexposed surface of the collector 30 and the exposed surfaces of thesecond polycrystalline extrinsic base portion 48.

The epitaxial base 60A and the first polycrystalline extrinsic baseportion 60B have a doping of the second conductivity type, which is theopposite conductivity type of the collector 30. A lower portion of thecavity 69 underneath the bottom surfaces of the second inner spacer 56and the first inner spacer 52 is partially filled with epitaxially grownbase material portions 60, which comprise the epitaxial base 60A and thefirst polycrystalline extrinsic base portion 60B.

The epitaxial base 60A comprises an epitaxial semiconductor materialthat is epitaxially aligned to the crystalline lattice structure of thecollector 30 because the epitaxial base 60A grows directly on thesurface of the collector 30. The first polycrystalline extrinsic baseportion 60B comprises a polycrystalline semiconductor material becausethe first polycrystalline extrinsic base portion 60B grows from thesidewall surfaces and the bottom surface of the second polycrystallineextrinsic base portion 48, which is polycrystalline. The firstpolycrystalline extrinsic base portion 60B grows concurrently with thegrowing of the epitaxial base 60A. The first polycrystalline extrinsicbase portion 60B contacts the epitaxial base 60A after the selectiveepitaxy. The first polycrystalline extrinsic base portion 60B and theepitaxial base 60A are formed by the same deposition process, andconsequently, comprise the same semiconductor material.

The first polycrystalline extrinsic base portion 60B contacts theentirety of sidewalls of the epitaxial base 60A. The secondpolycrystalline extrinsic base portion 48 contacts the entirety of outersidewalls of the first polycrystalline extrinsic base portion 60B.

Because the first polycrystalline extrinsic base portion 60B and thesecond polycrystalline extrinsic base portion 48 are formed at differentprocessing steps, the first polycrystalline extrinsic base portion 60Band the second polycrystalline extrinsic base portion 48 may comprisedifferent semiconductor materials. In one embodiment, the firstpolycrystalline extrinsic base portion 60B and the epitaxial base 60Acomprise a doped silicon germanium alloy, and the second polycrystallineextrinsic base portion 48 is a semiconductor material that is differentfrom the doped silicon germanium alloy, e.g., polysilicon having adoping of the second conductivity type.

Referring to FIG. 14, another selective epitaxy is performed to form anemitter 70 by selectively depositing a semiconductor material having adoping of the first conductivity type directly on the surface of theepitaxial base 60A. The emitter 70 contacts the epitaxial base 60A andthe first polycrystalline extrinsic base portion 60B, but does notcontact the second polycrystalline extrinsic base portion 48.

As in the selective epitaxy employed to grow the epitaxial base 60A, theselective epitaxy process employed for growing the emitter 70 deposits asemiconductor material only on semiconductor surfaces, i.e., only on theexposed surfaces of the epitaxial base 60A and the first polycrystallineextrinsic base portion 60B, but does not deposit any semiconductormaterial on dielectric surfaces. The emitter 70 fills the cavity 69. Inone embodiment, the top surface of the emitter 70 may be substantiallycoplanar with the top surface of the dielectric cap material mesaportion 51.

In one embodiment, the emitter comprises an epitaxial semiconductormaterial having an epitaxial alignment with the epitaxial base 60A. Inanother embodiment, the emitter 70 comprises a polycrystallinesemiconductor material.

Referring to FIG. 15, a sixth photoresist 67 is applied to the topsurfaces of the exemplary semiconductor structure and lithographicallypatterned. The sixth photoresist 67 covers the emitter-base region EBRand the NFET region NFETR, but does not cover the collector feedthroughregion CFTR or the PFET region PFETR. The portions of thestress-generating layer 64 and the buffer dielectric layer 62 in thecollector feedthrough region CFTR or the PFET region PFETR are removedselective to the semiconductor material in the semiconductor substrate8. The sixth photoresist 67 is subsequently removed. After removal ofthe sixth photoresist, the stress-generating layer 64 and the bufferdielectric layer 62 are present only in the NFET region NFETR.

Referring to FIG. 16, an activation anneal is performed to inducememorization of external stress in the semiconductor material portionbetween the source and drain regions 22 of the first conductivity typein the NFET region NFETR. Stress memorization technology employspatterned portions of the stress-generating layer 64 and an activationanneal so that localized stress is permanently “memorized” locallywithin a semiconductor substrate. The stress-generating layer 64 and thebuffer dielectric layer 62 are subsequently removed selective to thesemiconductor material in the semiconductor substrate 8. Because thelocal stress is permanently memorized in the semiconductor materialportion between the source and drain regions 22 of the firstconductivity type in the NFET region NFETR, the localized stress, whichis a tensile stress if the stress-generating layer 64 is atensile-stress-generating dielectric material, remains in the channel ofthe n-type field effect transistor in the NFET region NFETR even afterthe removal of the stress-generating layer 64. Typically, the secondouter spacer 57 is removed during the removal of the stress-generatinglayer 64, and the first outer spacer 53 is removed during the removal ofthe buffer dielectric layer 62.

Referring to FIG. 17, the dielectric gate caps 49 and the dielectric capmaterial mesa portion 51 are removed selective to the semiconductormaterials in the semiconductor substrate 8, the emitter 70, and thesecond polycrystalline extrinsic base portion 48. In case the dielectricgate caps 49 and the dielectric cap material mesa portion 51 comprisesilicon nitride, a wet etch in a hot phosphoric acid may be employed. Insome embodiments, the second gate spacers 58 may be removed during theremoval of the dielectric gate caps 49 and the dielectric cap materialmesa portion 51.

Referring to FIG. 18, yet another dielectric material layer may bedeposited and anisotropically etched to form spacers on verticalsurfaces of the exemplary semiconductor structure. For example, an upperspacer 72, a lower spacer 76, and outer gate spacers 74 may be formed.The upper spacer 72 and the lower spacer 76 are formed in theemitter-base region EBR, and constitute elements of the bipolar junctiontransistor structure. The upper spacer 72 contacts outer sidewalls ofthe first inner spacer 52, the lower spacer 76 contacts outer sidewallsof the second polycrystalline extrinsic base portion 76. Each of theouter gate spacers 74 contacts and laterally surrounds one of the firstgate spacers 54. Outer gate spacers 74 are formed in the NFET regionNFETR or in the PFET region PFETR, and constitute elements of MOStransistors. The upper spacer 72, the lower spacer 76, and the outergate spacer 74 comprise a second dielectric material and have a secondlateral width. The second dielectric material may be silicon nitride,and the second lateral width may be from 10 nm to 100 nm, althoughlesser and greater lateral widths may also be employed.

Referring to FIG. 19, various metal-semiconductor alloy regions, amiddle-of-line (MOL) dielectric layer 90 and contact vias are formed.The various metal-semiconductor alloy regions may include an emittermetal-semiconductor alloy region 87, a base metal-semiconductor alloyregion 86, a collector metal-semiconductor alloy region 84, gatemetal-semiconductor alloy regions 89, and source and drainmetal-semiconductor alloy regions 88. The various metal-semiconductoralloy region may be a metal silicide, a metal germanide, a metalgermano-silicide, or any alloy of am uunderlying semiconductor materialand a metal.

A middle-of-line (MOL) dielectric layer 90 comprising a dielectricmaterial is deposited over the various metal-semiconductor alloyregions. The MOL dielectric layer 90 may comprise, for example, a CVDoxide. The CVD oxide may be an undoped silicate glass (USG),borosilicate glass (BSG), phosphosilicate glass (PSG), fluorosilicateglass (FSG), borophosphosilicate glass (BPSG), or a combination thereof.The thickness of the MOL dielectric layer 90 may be from 200 nm to 500nm. The MOL dielectric layer 90 may also include a mobile ion diffusionbarrier layer (not shown) that prevents diffusion of mobile ions intothe semiconductor substrate 8. The mobile ion diffusion barrier layermay comprise silicon nitride. The MOL dielectric layer 90 is preferablyplanarized, for example, by chemical mechanical polishing (CMP).

Various contact via holes are formed in the MOL dielectric layer 90 andfilled with metal to form various contact vias. The various contact viasare formed on the various metal-semiconductor alloy regions. Forexample, the various contact vias may include an emitter contact via 97,at least one base contact via 96, a collector contact via 94, gatecontact vias 99, and source and drain contact vias 98.

While this invention has been particularly shown and described withrespect to preferred embodiments thereof, it will be understood by thoseskilled in the art that the foregoing and other changes in forms anddetails may be made without departing from the spirit and scope of thepresent invention. It is therefore intended that the present inventionnot be limited to the exact forms and details described and illustrated,but fall within the scope of the appended claims.

1. A semiconductor structure comprising: at least onemetal-oxide-semiconductor (MOS) transistor located on a first portion ofa semiconductor substrate, said at least one MOS transistor including ahigh dielectric constant (high-k) gate dielectric having a dielectricconstant greater than 3.9; and a bipolar junction transistor (BJT)located on a second portion of said semiconductor substrate, said BJTincluding a collector located in said semiconductor substrate andlaterally surrounded by at least one shallow trench isolation structure,an epitaxial base located on said collector, a first polycrystallineextrinsic base portion contacting an entirety of sidewalls of saidepitaxial base, a second polycrystalline extrinsic base portioncontacting an entirety of outer sidewalls of said first polycrystallineextrinsic base portion, and an emitter contacting said epitaxial baseand said first polycrystalline extrinsic base portion but not contactingsaid second polycrystalline extrinsic base portion.
 2. The semiconductorstructure of claim 1, wherein each of said at least one MOS transistorincludes a gate stack, and said gate stack includes at least one metalportion of a material that is selected from an elemental metal, ametallic alloy, a conductive metallic nitride, and a conductive metalliccarbide.
 3. The semiconductor structure of claim 1, wherein said BJTincludes a first inner spacer laterally surrounding said emitter, andeach of said MOS transistor includes a first gate spacer laterallysurrounding a gate stack and contacting sidewalls of said gate stack,and wherein said first inner spacer and said first gate spacer comprisea first dielectric material and have a same first lateral width.
 4. Thesemiconductor structure of claim 3, wherein said BJT further includes anupper spacer and a lower spacer, said upper spacer contacts outersidewalls of said first inner spacer, said lower spacer contacts outersidewalls of said second polycrystalline extrinsic base portion.
 5. Thesemiconductor structure of claim 4, wherein each of said MOS transistorincludes an outer gate spacer contacting sidewalls of said first gatespacer.
 6. The semiconductor structure of claim 5, wherein said upperspacer, said lower spacer, and said outer gate spacer comprise a seconddielectric material and have a second lateral width.
 7. Thesemiconductor structure of claim 4, wherein a bottommost surface of saidupper spacer is vertically spaced from a topmost surface of said firstpolycrystalline extrinsic base portion by a thickness of said secondpolycrystalline extrinsic base portion.
 8. The semiconductor structureof claim 3, wherein inner sidewalls of said second polycrystallineextrinsic base portion contact a lower portion an outer sidewall of saidfirst inner spacer.
 9. The semiconductor structure of claim 8, wherein abottom surface of said first inner spacer is vertically spaced from atop surface of said first polycrystalline extrinsic base portion by athickness of said second polycrystalline extrinsic base portion.
 10. Thesemiconductor structure of claim 9, wherein one of said at least one MOStransistor includes a gate stack, and said gate stack includes asemiconductor material portion that has a same thickness as, and a samecomposition as, said second polycrystalline extrinsic base portion. 11.The semiconductor structure of claim 8, wherein an inner sidewall ofsaid first polycrystalline extrinsic base portion laterally protrudesinward from said outer sidewall of said first inner spacer.
 12. Thesemiconductor structure of claim 3, wherein said BJT includes a secondinner spacer that contact inner sidewalls of said first inner spacer andsaid emitter.
 13. The semiconductor structure of claim 12, wherein abottom surface of said second inner spacer is coplanar with a bottomsurface of said first inner spacer.
 14. The semiconductor structure ofclaim 1, wherein one of said at least one MOS transistor includes a gatestack, and said gate stack includes said high-k gate dielectric and asemiconductor material portion that has a same thickness as, and a samecomposition as, said second polycrystalline extrinsic base portion. 15.The semiconductor structure of claim 14, wherein said gate stack furtherincludes a metal portion in contact with said high-k gate dielectric,another semiconductor material portion in contact with said metalportion, and said semiconductor material portion.
 16. The semiconductorstructure of claim 1, wherein said BJT includes a subcollector and asubcollector feedthrough, said subcollector contacts said collector,said subcollector feedthrough contacts said subcollector, and bottomportions of source and drain regions of one of said at least one MOStransistor have a same doping as said subcollector feedthrough.
 17. Thesemiconductor structure of claim 1, wherein said first polycrystallineextrinsic base portion and said second polycrystalline extrinsic baseportion comprise different semiconductor materials.
 18. Thesemiconductor structure of claim 17, wherein said first polycrystallineextrinsic base portion and said epitaxial base comprise a samesemiconductor material.
 19. The semiconductor structure of claim 18,wherein said first polycrystalline extrinsic base portion and saidepitaxial base comprise a doped silicon germanium alloy.
 20. Thesemiconductor structure of claim 19, wherein said second polycrystallineextrinsic base portion is a semiconductor material that is differentfrom said doped silicon germanium alloy.